There are a few types of fans being marketed to exhaust corrosive or high temperature gas. The three main types of fans that are currently produced are the utility set fan (FIGS. 1a and 1b), the belt driven tube fan (FIG. 2), and the bifurcated fan (FIG. 3). These prior art fans are generally expensive and/or cumbersome and are discussed in further detail below.
A utility set fan 100, as shown in FIG. 1a, usually sits on a frame, and the fan wheel is directly driven by a motor with the fan housing wall separating the two. The fan wheel is centrifugal-type, with a scroll housing that forces the designer to exhaust the gas at a ninety degree angle from the inlet gas stream (FIG. 1b). Adding the ninety degree angle can be very cumbersome for the ducting designer to work into a duct layout.
A belt driven tube fan 200, as shown in FIG. 2, utilizes a straight-through tube design that can be placed anywhere in the ducting system, unlike the utility set fan discussed above. However, the motor must be placed outside of the air-stream to avoid over-heating or corrosion by the exhaust gasses. To move the motor outside of the air-stream, a belt driven pulley system is used to drive the fan wheel. Belts are undesirable, as they are difficult to maintain and inefficient.
A bifurcated fan 300, as shown in FIG. 3, is a hybrid of the utility set fan and the belt driven tube fan. The bifurcated fan places the motor inline with the air-stream in a tube-like manner, but protects the motor by bifurcating the gas stream and creating a motor housing which is outside of the gas stream. While this solves some problems associated with the utility set fan and the belt driven tube fan, the fan size required is often larger than the utility set or the tube fan due to the enormous pressure drop created by the motor housing.